Organometallic Complexes for Nonlinear Optics. 8.1Syntheses and Molecular Quadratic Hyperpolarizabilities of Systematically Varied (Triphenylphosphine)gold σ-Arylacetylides: X-ray Crystal Structures of Au(C⋮CR)(PPh3) (R = 4-C6H4NO2, 4,4‘-C6H4C6H4NO2)

The series of complexes Au(C⋮CR)(PPh 3 ) (R = Ph ( 2 ), 4-C 6 H 4 NO 2 ( 3 ), 4,4‘-C 6 H 4 C 6 H 4 NO 2 ( 4 ), ( E )-4,4‘-C 6 H 4 CH CHC 6 H 4 NO 2 ( 5 ), ( Z )-4,4‘-C 6 H 4 CH CHC 6 H 4 NO 2 ( 6 ), 4,4‘-C 6 H 4 C⋮CC 6 H 4 NO 2 ( 7 ), 4,4‘-C 6 H 4 N CHC 6 H 4 NO 2 ( 8 )) have been synthesized by reaction of AuCl(PPh 3 ) with the corresponding acetylene and methoxide, and complexes 3 − 8 have been structurally characterized. The molecular first hyperpolarizabilities for the complexes have been determined by hyper-Rayleigh scattering at 1064 nm. Introduction of the nitro substituent (in proceeding from 2 to 3 ) leads to a significant increase in nonlinearity. Experimental β values increase as 3 < 4 < 6 ≈ 7 < 8 < 5 consistent with nonlinearity increasing with (i) chain lengthening, (ii) replacing biphenyl ( 4 ) or yne linkage ( 7 ) by ene linkage ( 5 ), (iii) replacing ( Z )-ene stereochemistry ( 6 ) with ( E )-ene stereochemistry ( 5 ), and (iv) ene linkage ( 5 ) being more efficient than imino linkage ( 8 ). The same trend is observed with two-level-corrected data. A linear correlation of both experimentally-determined and two-level-corrected nonlinearities of the acetylides with precursor acetylenes is observed.